1. Field of the Invention
The present invention relates to a three-dimensional geometry processing system and method, and more particularly to a three-dimensional geometry processing system and method for a solid computer-aided design (CAD) apparatus restricted in surface representations to import solid data in boundary representations.
2. Discussion of the Background
Practical three-dimensional computer-aided design (CAD) apparatuses mainly deal with solid data. Most of the three-dimensional CAD apparatuses deal with the solid data in boundary representations. The three-dimensional CAD apparatuses generally exchange data in a standard format such as IGES. Generally, when the standard format is used for data exchange, a system which receives data joins surfaces to generate solid data from information on surfaces only. Recently, solid data can be represented in the standard format, and the solid data can be exchanged as is.
Exchanging solid data mainly involves two technical difficulties. The difficulties are related to accuracy and restriction in representations of a CAD apparatus for receiving data. When the CAD apparatus has relatively high accuracy, there can be an exchanging data problem related to accuracy. However, a modification mechanism has been developed to overcome the difficulty related to accuracy. For example, a solid data modification method is available. In the solid data modification method, when there is a deviation from a tolerable range of a target system or a gap at a vertex portion or between a boundary curve and a surface, the gap between an end point and another end point, or between the boundary curve and the surface is filled so that data can be within the tolerable range of the target system having high accuracy. In detail, coordinates of end points of boundary curves of faces representing a shell of a solid are expected to meet at the vertex portion. When the gap between the coordinates is out of the tolerable range of the target system, however, a coordinate of a vertex is determined within the tolerable range based on the end points of the boundary curves gathering at the vertex portion and information of coordinates on a surface corresponding to the end points. Then, the boundary curves are modified so as to have the coordinate of the vertex as the end points thereof. Further, when the gap between the boundary curve and the surface is out of the tolerable range, a geometry of the surface is changed so that the boundary curve and the surface mate within the tolerable range of the target system.